Non-volatile multi-bit memory cells are programmed by hot electron
programming and erased by high voltage tunneling, or by the use of a
lower voltage Metal-Insulator-Metal (MIM) Diode carrier generation method
and technology called the Tunnel-Gun (TG), in which the use of a Nitride
layer or a silicon-nodule layer having location-specific charge storage
elements with no spreading allows easy implementation of multi-bit
technology. If charges are stored in the traps in the Nitride storage
layer, an Oxide Nitride Oxide is used as the storage element. If charges
are stored in layer of discrete silicon-nodules separated by a thin
insulating film, an Oxide silicon-nodule Oxide storage element is used as
the storage layer.